Abstract

Liposomes were first described about 40 years ago (Bangham et al., 1965). At first they were used to study biological membranes. The ability of liposomes to encapsulate different materials has given rise to the relatively recent use of liposomes as carriers for the incorporation of active ingredients. These processes, which are known as liposomal delivery systems (LDS), have shown remarkable progress over the years. However, in spite of intense scientific activities all over the world, the first drug based on liposomes was introduced to the market only in 1996 (Lasic, 1996). Liposomes are self-assembled colloidal particles that occur naturally and can be prepared artificially. They are microscopic spherical vesicles formed by phospholipids dispersed in water. When amphiphatic lipid molecules containing polar heads and hydrophobic hydrocarbon tails are suspended in an aqueous medium, they can associate spontaneously to form bilayer vesicles. The basic structure of liposomes is similar to biological cell membranes, thus making them very attractive as delivery vehicles including for topical drug delivery. The resulting vesicles comprise an aqueous compartment surrounded by one or more lipid bilayers, which are relatively impermeable to the entrapped substances (Storm and Crommelin, 1998, Gregoriadis, 1993).